This application claims the priority of German application 196 27 796.5 filed in Germany on Jul. 10, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and a device for monitoring the position of a variable valve control.
In internal combustion engines equipped with a variable valve control, it is necessary to monitor the function of this variable valve control at regular intervals. Known monitoring methods determine the position of a component used to adjust the valve control in order thus to determine the current position of the valve control. However, a monitoring method of this kind provides only a general idea of how the valve control is being controlled at a given moment.
Methods are also known for detecting when combustion does not occur in internal combustion engines, said methods being based on an analysis of the curve of the angular velocity of the crankshaft during one working cycle of a cylinder of the internal combustion engine. Failure of combustion to occur results in particular changes in the speed curve by comparison to the normal state. A method of this kind is described for example in German Patent Document DE 40 09 285 A1.
On the other hand, an object of the invention is to provide a method and a device for monitoring the position of a variable valve control in which the construction cost is reduced.
This object is achieved by providing a system and a method for carrying out the following steps:
detecting a nonuniformity in the rotational speed of a crankshaft in an internal combustion engine; PA1 evaluating the nonuniformity of the rotational speed of the crankshaft in terms of the combustion state of the engine; and PA1 associating the combustion state with a position of the variable valve control.
The invention is based on the fact that the combustion process in the individual cylinders is also dependent on the operating behavior and/or operating state of a variable valve control. In particular, during shifting of a variable valve control, the combustion state of the individual cylinders changes considerably. This combustion process and/or its change can be detected using the analysis, known of itself, of the angular velocity of the crankshaft, more specifically the uniformity of the rotary movement of the crankshaft. Information about the operating state of the variable valve control is then obtained from the combustion process and/or the uniformity of rotation of the crankshaft as detected.
The invention is associated with the particular advantage that in addition to reducing the cost of measurement technology, since a sensor for the angular position of the crankshaft is provided in any case in modern internal combustion engines, only the operating state of a variable valve control is determined on the basis of the combustion state of the engine as influenced by the variable valve control. This is especially important if monitoring of the variable valve control is required for monitoring and detecting the maintenance of legally prescribed exhaust values (OBD II). In addition to reducing the cost of measurement technology, the invention offers the additional advantage that both control and monitoring of the variable valve control take place in the engine control device. Since this engine control device receives the signal from the crankshaft angle sensor in any event, the invention can be implemented within an engine control device without additional leads or pins being required on the control device.
Thus it is proposed according to certain preferred embodiments of the invention to conduct and evaluate the analysis of the uniformity of the rotational speed of the crankshaft in a cylinder-specific manner, and from this to determine the combustion state, once again in a cylinder-specific manner, and to compare it with the combustion state of the other cylinders. The deviation of the combustion state of an individual cylinder from the average value of the combustion states in all the cylinders then provides information about any improper behavior of the variable valve control with respect to individual cylinders.
The design of the invention is facilitated if, as is also proposed according to certain preferred embodiments of the invention, the crankshaft angle sensor signal is evaluated by the irregularity of the rotational speed of the crankshaft that is determined being compared with boundary values that are stored as normal or reference values in a memory and depend on the load and rotational speed of the internal combustion engine.
Finally, it is proposed according to certain preferred embodiments of the invention, to plot the curve of the irregularities in the rotational speed of the crankshaft to evaluate the crankshaft angle sensor signal and then to compare them with a given curve. Since the curve of the nonuniformity of the rotational speed of the crankshaft is critical in this respect, this evaluation is largely inconspicuous by comparison with external disturbances. For further simplification, it can be provided that this evaluation be performed only when the position of the variable valve control is changed. In this way, the control device is relieved of this monitoring task for the rest of the time.
Monitoring the variable valve control according to the invention can be presented as part of a program-controlled control device for the vehicle (method), and with the same advantages, and as a discrete circuit (device).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.